A circuit board used in a vehicle headlight comprises a vehicle-mounted battery module and a light-emitting diode. The vehicle-mounted battery module provides a driving current to the light-emitting diode to control the light-emitting diode to emit light. The rated power of the light-emitting diode is small, according to P=U2*S/(ρL) (where P represents power, U represents voltage, ρ represents conductor resistivity, and L represents resistance length), and when U, ρ, L are invariant, S is smaller. That is, circuit connecting electrically the vehicle-mounted battery module and the light-emitting diode carries fine-scale lines. When a high power current runs through the fine-scale lines a large amount of heat is produced, the heat will damage the light-emitting diode.